During certain types of medical surgery or treatment, an introducer is used to access the vascular system of a patient. The introducer is inserted through the wall of a blood vessel in order to obtain access to the vascular system and may thereafter be used for guiding medical instruments such as catheters, guide wires and the like.
After completion of the medical procedure, there will be an incision or a wound in the wall of the blood vessel corresponding to the size of the introducer. The bleeding from the wound, which is the result of such a surgical operation, can be stopped by applying direct pressure on the wound. However, applying direct pressure on the wound will require assistance of additional medical personnel and may also restrict the flow of blood through the vessel.
Another, more sophisticated, basic method for sealing such a percutaneous puncture in a vessel involves the positioning of an intra-arterial occluder against the inner wall of the vessel. Different examples of this basic method may be found in U.S. Pat. Nos. 4,852,568; 4,890,612; 5,021,059; 5,350,399 and 5,593,422. The intra-arterial occluder can be held taut against the inner vessel wall by a filament or suture only, as described in U.S. Pat. No. 4,852,568, or an extra-arterial occluder can be threaded over the suture and positioned against the outer wall of the vessel to secure the intra-arterial occluder, as disclosed in U.S. Pat. No. 5,593,422. In U.S. Pat. Nos. 4,890,612 and 5,021,059, the intra-arterial occluder, which is positioned by means of a suture or a filament, is supplemented with a plug, which is positioned in the puncture channel. The sealing device disclosed in U.S. Pat. No. 5,350,399 comprises an intra-arterial occluder and an extra-arterial occluder.
The different materials from which these intra-arterial and/or extra-arterial occluders are made are not the main subject matters of the inventions disclosed in the patents above. Usually, the material for such an occluder is characterized as being a resorbable or absorbable, biocompatible or biodegradable material. In U.S. Pat. Nos. 4,890,612 and 4,852,568, a preferred material for the occluder is GELFOAM, a gelatin sold by Johnson & Johnson, while a suggested material in U.S. Pat. No. 5,021,059 is MEDISORB, a resorbable lactide/glycolide polymer sold by E.I. DuPont de Nemours, Inc. In a preferred embodiment of the invention according to U.S. Pat. No. 5,593,422, the occluder is made from a material that comprises collagen or alginate. It is well known in the art that the materials used in these types of occluders degrade inside the body by means of biological and/or chemical processes. This means that the materials, which are often based on a polymeric structure, undergo reaction as they degrade and are absorbed. Such reactions can be, for example, hydrolysis including hydrolysis mediated by enzymes. The biological and chemical degradation processes typically lower the molecular weight of the polymeric structure, which increases solubility and absorbability. Furthermore, for these types of occluders, it is equally well known in the art that the degradation time, i.e. the time it takes for the body to absorb an occluder made of the material in question, typically is several weeks, months or even years. U.S. Pat. No. 5,593,422 gives a degradation time of a few weeks, while U.S. Pat. No. 4,890,612 mentions a degradation time of approximately 45 days. U.S. Pat. No. 5,350,399 discloses that degradable materials should “slowly dissolve”. Additional background on absorbable materials is set forth in WIPO Publication WO 01/40348.
One reason for using an absorbable material in an occluder is to avoid or minimize the risk of having an inflammatory response in the tissue surrounding the occluder. This inflammation can be the result of a mechanical damage on the vessel wall caused by mechanical wearing of the occluder during the natural movements of the vessel. From this point of view, the shorter time before the complete degradation of an occluder, the less is the risk of having an inflammation in the tissue surrounding the occluder. In this context it should be noted that when only external pressure is applied on the puncture wound, i.e. without using any of the intra-arterial or extra-arterial occluders described above, the actual compression time can be as short as fifteen minutes, although the patient usually is kept immovable for a few hours. This means that the occluders known in the state of the art remain in the body an unduly long time. If another medical operation is going to be performed at the same operation site as the first operation, it is a disadvantage to have an occluder already inserted in the vessel, since this occluder can obstruct the medical operation itself and may also make it impossible to safely position a new occluder at (or near) the same position.
A problem with the materials of these known seals is that different parts of the seals will be in different states of degradation during the absorption process. Therefore the seals become increasingly porous and will exhibit lower rupture strength, and due to the blood flow in the vessel there is a risk that pieces of different sizes of the seal come loose and follow the blood flow to more narrow passages where the parts can get stuck and restrict or even prevent the blood flow. Of course this could be serious for the patient and may necessitate an operation.
Furthermore, a suture or filament that is holding the seal in place is rather thin in comparison with a seal and thus there is a risk that the suture or filament ruptures through a seal being in more or less degraded state. Also in such case the seal will come loose in the vessel where it can follow the blood flow as described above.
A further problem with the known seals is that around the seal cells and tissues develop on and adhere to the surface, so that the seal becomes encapsulated in a sac-like tissue material. Inside the sac-like encapsulating tissue, the seal degrades. Then the sac-like encapsulating material also regresses. For a conventional seal, this means that the seal and the tissue that develops thereon occupy more and more of the available space inside the vessel until the process is reversed, i.e. when seal starts to degrade and the encapsulating tissue starts regress. Furthermore, this problem may be enhanced by the fact that many conventional seals are made of materials that swell in the fluid inside a vessel. The ingrowth of the encapsulating tissue can restrict blood flow temporarily or even permanently, particularly if the encapsulating tissue fails to regress properly. Also, if the tissue does not grow on the surface of a conventional seal, then the seal can potentially come loose inside the blood vessel.
The encapsulating of the seal is needed in the known seals described above. Without the encapsulation the breaking down of the seal would probably cause parts of the seal to come loose and drift away with the blood flow. Thus the known seals rely on the encapsulating effect. However, it is not safe to rely on this effect since it could vary between individuals, and furthermore even small rests of certain materials, such as Teflon®, from the manufacturing of the seal could be left on the surface of the seal and prevent the adhering of the cells.